Article

New antiviral pathway that mediates hepatitis C virus replicon interferon sensitivity through ADAR1

CBER/FDA, HFM-448, 8800 Rockville Pike, Bethesda, MD 20892, USA.
Journal of Virology (Impact Factor: 4.65). 06/2005; 79(10):6291-8. DOI: 10.1128/JVI.79.10.6291-6298.2005
Source: PubMed

ABSTRACT While many clinical hepatitis C virus (HCV) infections are resistant to alpha interferon (IFN-alpha) therapy, subgenomic in vitro self-replicating HCV RNAs (HCV replicons) are characterized by marked IFN-alpha sensitivity. IFN-alpha treatment of replicon-containing cells results in a rapid loss of viral RNA via translation inhibition through double-stranded RNA-activated protein kinase (PKR) and also through a new pathway involving RNA editing by an adenosine deaminase that acts on double-stranded RNA (ADAR1). More than 200 genes are induced by IFN-alpha, and yet only a few are attributed with an antiviral role. We show that inhibition of both PKR and ADAR1 by the addition of adenovirus-associated RNA stimulates replicon expression and reduces the amount of inosine recovered from RNA in replicon cells. Small inhibitory RNA, specific for ADAR1, stimulated the replicon 40-fold, indicating that ADAR1 has a role in limiting replication of the viral RNA. This is the first report of ADAR's involvement in a potent antiviral pathway and its action to specifically eliminate HCV RNA through adenosine to inosine editing. These results may explain successful HCV replicon clearance by IFN-alpha in vitro and may provide a promising new therapeutic strategy for HCV as well as other viral infections.

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    • "ADAR1 was also known to edit double-stranded RNA found in the measles virus, which inhibited virus assembly and release from cells, leading to a persistent infection and development of fatal neuropathic measles infection (Horikami and Moyer, 1995). Taylor, et al. (2005) showed that ADAR1-induced viral RNA editing inhibited Hepatitis C viral replication (Taylor et al., 2005). Recently Suspene et al. (Suspene et al.) have shown ADAR1 induced mutation in seasonal influenza and attenuated measles viruses. "
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    ABSTRACT: We examined the antiviral activity of ADAR1 against HIV-1. Our results indicated that ADAR1 in a transfection system inhibited production of viral proteins and infectious HIV-1 in various cell lines including 293T, HeLa, Jurkat T and primary CD4+ T cells, and was active against a number of X4 and R5 HIV-1 of different clades. Further analysis showed that ADAR1 inhibited viral protein synthesis without any effect on viral RNA synthesis. Mutational analysis showed that ADAR1 introduced most of the A-to-G mutations in the rev RNA, in the region of RNA encoding for Rev Response Element (RRE) binding domain and in env RNA. These mutations inhibited the binding of rev to the RRE and inhibited transport of primary transcripts like gag, pol and env from nucleus to cytoplasm resulting in inhibition of viral protein synthesis without any effect on viral RNA synthesis. Furthermore, ADAR1 induced mutations in the env gene inhibited viral infectivity.
    Virology 11/2011; 422(2):265-77. DOI:10.1016/j.virol.2011.10.024 · 3.28 Impact Factor
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    • "Protein kinase R (PKR) for example, phosphorylates the alpha subunit of the eukaryotic initiation factor (eIF)-2 leading to suppression of translational processes (Gale, Jr. et al. 1999; Pflugheber et al. 2002). The RNA-specific adenosine deaminase 1 (ADAR1) binds to dsRNA resulting in destabilization of secondary structures (Taylor et al. 2005). The antiviral function of 2′-5′ oligoadenylate synthetases (2'-5' OAS) is mediated by the activation of the latently expressed endoribonuclease RNaseL, which induce degradation of viral and cellular RNA (Silverman, 1994; Zhou et al. 1997). "
    Viral Hepatitis - Selected Issues of Pathogenesis and Diagnostics, 11/2011; , ISBN: 978-953-307-760-4
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    • "The HCV replicon system has provided a valuable experimental strategy to study HCV RNA replication and innate antiviral immunity (Appel et al., 2006). Evidence consistent with an antiviral role of ADAR1 emerged when it was found that IFNα treatment of HCV RNA replicon-containing cells inhibited HCV viral RNA production, and that the siRNA-mediated knockdown of ADAR1 or the inhibition of ADAR (and PKR) activity by adenovirus VAI RNA stimulated HCV viral RNA production and reduced inosine-containing viral RNA (Taylor et al, 2005). "
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    ABSTRACT: A-to-I RNA editing, the deamination of adenosine (A) to inosine (I) that occurs in regions of RNA with double-stranded character, is catalyzed by a family of Adenosine Deaminases Acting on RNA (ADARs). In mammals there are three ADAR genes. Two encode proteins that possess demonstrated deaminase activity: ADAR1, which is interferon-inducible, and ADAR2 which is constitutively expressed. ADAR3, by contrast, has not yet been shown to be an active enzyme. The specificity of the ADAR1 and ADAR2 deaminases ranges from highly site-selective to non-selective, dependent on the duplex structure of the substrate RNA. A-to-I editing is a form of nucleotide substitution editing, because I is decoded as guanosine (G) instead of A by ribosomes during translation and by polymerases during RNA-dependent RNA replication. Additionally, A-to-I editing can alter RNA structure stability as I:U mismatches are less stable than A:U base pairs. Both viral and cellular RNAs are edited by ADARs. A-to-I editing is of broad physiologic significance. Among the outcomes of A-to-I editing are biochemical changes that affect how viruses interact with their hosts, changes that can lead to either enhanced or reduced virus growth and persistence depending upon the specific virus.
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